JPH03229258A - Reducing of pinhole for resist film - Google Patents

Abstract

PURPOSE: To make it possible to form a photoresist film free from pinholes by precipitating an org. coating material on a conductive substrate and acting the continuous vibrating force of the energy sufficient for removing the air bubbles sticking to the substrate on the substrate. CONSTITUTION: If, for example, the substrate 5 is immersed into the electrodeposition bath of an anionic photosensitive resin, compn. an anode is installed to the substrate 5 and a cathode 7 in the bath. The anionic photosensitive resin compsn. is precipitated by DC. A device 1 is connected to the outer side of an electrodeposition tank 2 by such a method that generates the vibration of frequency and amplitude sufficient for expelling the air bubbles generated on the surface of the substrate 5 in the precipitation process of the film. As a result, the uniform precipitation of the photoresist on the conductive substrate is made possible.

Description

DETAILED DESCRIPTION OF THE INVENTION INDUSTRIAL APPLICATION The present invention relates to a method for achieving pinhole-free organic coatings applied to conductive substrates during M deposition processes. In a preferred embodiment, the present invention relates to uniformly depositing photoresist on a conductive substrate in the process of making printed circuit boards, and the applied force 1 force is applied to the substrate during the deposition process. It will be done.

BACKGROUND OF THE INVENTION Imaging on a substrate is typically accomplished by coating the substrate with a positive or negative photoresist material. It has been found that adhesion to the substrate is improved when the photoresist material is applied by electrodeposition.

The application of photosensitive layers by electrodeposition is not new, as shown in the prior art below, for example, U.S. Pat. No. 4,632,900, Japanese Published Patent No.
No. 11601 and U.S. Patent No. 4.592.816. Photoresist is 1! The substrate to be deposited must be charge-accepting and is preferably either a rigid metal sheet or a laminate with a metal surface. When forming printed circuits that are electrically connected by through-holes on both sides of a laminate with metal surfaces, it is necessary to protect the exposed metal containing the through-holes from subsequent processing.
Usually this is accomplished by coating the laminate with a photoresist film. The photosensitive resin composition of the film may be anionic or cationic as long as it forms a continuous film on the conductive substrate by electronic observation.
A preferred method uses a cationic resin system, where the substrate to be coated acts as a cathode and the anode is placed in an electrodeposition bath. The method is also easily applicable to anionic resin systems, where the substrate acts as an anode and the cathode is placed in an electrodeposition bath.

It is essential that the film be continuous in order to produce the sharp, high resolution images needed to make high density printed circuit boards or other optically imaged metals. The drawback in this case is that defects, particularly pinholes, are unavoidable when forming such a continuous film. The source of these pinhole defects is during the electrodeposition process during the coating process. This occurs due to the presence of electrolytic gases generated at the poles and the force of water pressure in the bath water supply system.

The occurrence of these pinholes increases over time and with the number of substrates being processed due to the accumulation of electrolytic gas floating in the upper layer of the emulsion and not dissipating. On the contrary, the electrolytic gas adheres to the substrate and interferes with film coating in areas with bubbles. These pinholes are the main cause of warping of lines and breakage of inner layer circuits during the manufacturing process of multilayer printed circuit boards. Another problem caused by pinhole defects is that the metal in the defective areas may be etched or plated in the areas where these defects occur. Voltage, i! Flow,
Temperature and 4T4. The factors that give W'r￥9 to electrodeposition, such as rate, are tl! Although the amount of pinholes observed is influenced by the amount of pinholes detected, the key to suppressing pinhole formation is to regulate the coating thickness range, which affects overall yield, as well as influencing coating time, uniformity, and appearance. .

Some clues to the problem of modifying the visibility and performance of films can be found in the prior art Japanese Published Patent No. 56-156745 M, which describes a method for treating iron surfaces. In this method, an ultrasonic diaphragm is immersed in a molten plating alloy solution to form an alloy film on the surface of the iron plate. The ultrasonic wave impinges vertically on the gold Ix plate, causing a large radial pressure.

The presence of magnesium destroys and dissipates any oxidation deposits on the metal surface. The application of ultrasound to electrolytic plating has been described as a method that increases the commonly used if current density several times. The invention presented herein is not affected by current density, unlike the above-mentioned patent; varying the current density in the electrodeposition process has significant effects on coating uniformity, deposition rate and, as a result, coating performance. have a negative effect.

Another Japanese Patent Publication No. 51-149833 describes a plating method that applies vibrations, where the vibrations change the equipotential lines between the anode and cathode. In a preferred method, an electric current is passed between the anode and the cathode, and the anode is caused to oscillate up and down, back and forth, or side to side, or a combination of these movements. Changes in the equipotential between the cathode and the anode cause variations in the conditions for electrolytic deposition of the plating layer. The invention presented herein differs from the above-mentioned patent in that electrode movement is minimal and the vibrations are applied directly to the substrate being coated. Furthermore, the invention relies on the fact that the potential between the anode and cathode does not change. Again, variations in one equipotential will affect the current density and, as mentioned above, will have an adverse effect on the coating.

The present invention differs from the above invention in that the electrodeposition process is typically carried out at higher voltages than electrolytic coating. The voltage for electrolytic plating is usually in the range of 6-24 volts, but in electrodeposition the voltage can range up to 400 volts. This means that the higher the voltage, the more water is electrolyzed and the more water is removed from the substrate surface. This means that the problems associated with gas removal become more complex. The time required for plating is significantly longer than for electrodeposition, which provides extensive opportunities for removing gas from the substrate surface by various means, including current oscillations and reverse plating. In the electrodeposition process, the substrate is coated under conditions of about 10 seconds.

As described in the prior art, the use of such ultrasonic transducers cannot directly be applied to electrodeposited compositions, since ultrasonic vibrations are highly susceptible to the stability of the coating emulsion.

The present invention discloses a method for removing air bubbles from a substrate surface, otherwise air bubbles may be removed. FJ aggregates and destroys the adhesion of the electrophoretic film to the substrate.
This can be accomplished without changing other factors that negatively impact membrane performance.

[Problem M that the invention seeks to solve]

The invention disclosed herein relates to a method of achieving pinhole-free photoresist coatings on conductive substrates in a process in which the coating is applied in one process. A method of eliminating pinhole defects is achieved by using a vibrating device that can be easily connected to existing equipment and does not limit the coating process in any way.1 Equipment used to carry out the present invention teeth.

It is possible to generate a frequency of 60 to 3 (more than 1,000 vibrations per minute). The device is attached to an electrodeposition device such that the vibrations are directed at the substrate to be coated.

SUMMARY OF THE INVENTION In practicing the present invention, a method is provided for achieving pinhole-free photoresist coatings on conductive substrates.

The board is rPrinted C1rcuits Handboo by C1yde F. Coombs, Jr.
A copper clad laminate prepared by the method described in Chapter 2 of KJ 2nd Edition, McGraw-Hill, 1979. For other suitable boards.

As described in Chapter 23 of the above reference, it includes a board prepared by laminating multilayer boards for the production of printed circuit boards with through holes, both of which are incorporated herein by reference. It is. Other suitable substrates include flexible metal foils, metal sheets or other conductive substrates.

The substrate can be flat or of various shapes.

The thickness varies.

The photoresist coating used in the present invention can be used insofar as it forms a continuous film on the substrate by means of electrodeposition.
Further, it may be anionic or cationic as long as it is dissolved by the developer in the next process.

For example, an electrodeposition bath having an anionic photosensitive resin composition is produced by copolymerizing an α,β-ethylenically unsaturated compound having an acidic group with a copolymerizable monomer having a hydroxyl group. A quinone diazide compound is added to the hydroxyl group of the polymer to perform a Nisderization reaction, and the acidic group from the a, β-ethylenically unsaturated compound is neutralized with an alkali substance. It is prepared by dispersing the polymer in water.

The electrodeposition bath having a cationic resin composition is prepared by copolymerizing a monomer having at least one amino group.

A photoinitiator is added to some of the amino groups in the obtained copolymer, the remaining amino groups in the copolymer described in 1g are neutralized with an acidic substance, and the thus obtained neutralized polymer is It is prepared by dispersing it in water.

The above general description of the electrodeposition bath is illustrative and is not limited to such bath compositions.

Other coating compositions that can be used in sophisticated processes are described in U.S. Pat. No. 4.59, incorporated herein by reference.
No. 2.816 and U.S. Pat. No. 4.632.900.

The electrodeposition bath of the present invention may contain a colorant and a colorant as required.
Other additives may also be included, such as analogs used in f-coating.

Examples of typical electrodeposition bath compositions are shown in Table 1, where relative concentrations are expressed in weight relative to 100 parts of polymer M.

Polymer 100 Solvent 0-70 Unsaturated 30-50 Photoinitiator 3-8 Acid 1-3 Water
In order to apply the anionic or cationic photosensitive resin composition onto a 90-row 2600 copper metal plated plate, copper-clad laminate board, or other conductive substrate, the present invention uses conventional electrodeposition means. is possible.

For example, when a substrate is immersed in an electrodeposition bath of an anionic photopolymer composition, an anode is connected to the substrate and a cathode is placed in the bath, and a direct current flows between the electrodes, thereby causing an anionic photopolymer composition. A photosensitive resin composition is deposited on the substrate.

If a cationic resin composition bath is used, the anode and cathode are connected in reverse and a similar procedure is carried out to obtain a continuous film of bicationic resin composition.

In the above process, this sophisticated and improved method for producing pinhole-free coatings is designed to generate vibrations of sufficient frequency and amplitude to eliminate air bubbles generated on the surface of the substrate during the coating deposition process. The vibrations are generated in a reciprocating or rotary manner, including coupling the device to the outside of the 1F tank.

For example, if a vibration motor is used, it is an electric motor or a pneumatic turbine motor. The motor should be connected waterproof in either position and allow speed adjustment. Electric motor: 1.600 per minute
A vibration rate of ~3.200 times should be possible.

The pneumatic turbine motor should be capable of generating vibration rates of 12,000 to 15,000 vibrations per minute at an air flow of 60 psi. 60 to 30,000. The preferred frequency is 3.000 vibrations per minute or more. Other devices may be used to generate the necessary vibrations (and the practice of the invention is not limited to the examples described herein).

The equipment used is mounted in such a way that vibrations are isolated and transmitted only directly to the substrate. FIG. 1 shows an example of how the invention may be carried out. For example, the motor (1) is mounted on the outside of a tank (2) by means of a yoke (3) placed above the tank. The motor is positioned equidistant from both ends of the tank. The yoke is isolated from the tank by using a vibration-absorbing rubber cushion (4), which does not transmit vibrations to the tank, but only to the substrate (5). The tIF tank contains an electrophoretic coating bath (6) as well as electrodes (7), the substrates acting as electrodes of opposite charge.8 The substrates are placed in the bath by being attached to the flight bar (8);
The flybar consists of two spring-loaded clamps (10) attached to the yoke by flanges (10).
9) is held in place. The flight bar is assembled in such a way that the substrate is held in place by a cleave (Ill), which ensures conductivity and also eliminates air bubbles (12) generated by water electrolysis during the electrodeposition process. This ensures that vibrations are transmitted directly to the substrate.

To reiterate, the above is merely one example of equipment that may be used to practice the present invention. Other examples of devices that can generate the necessary vibrations are orbital Santas, impact hammers, vibratory engravers or hammers. It is necessary to mount the device in the same orientation as the flight bar so that the vibrations are transmitted directly to the board. The device is attached to the flight bar by bolting, clamping, or any other method that transmits vibrations in the direction of the flight bar.

Other methods of directing vibration only to the flight bar include mounting the vibration device on any upper support so that it is in continuous contact with the flight bar.

The table below illustrates the reduction in pinholes by implementing the present invention.

1S1 Substrate: llll horizontal laminate: Electrodeposition photoresist composition (as shown in Table 1) Voltage: 75 volts Residence time = 30 seconds Control manual 7-stroke resistance (on flight bar) 1 time/sec) Vibration engraving machine (set opposite to flight 7+-) Impact hand 7- (direction of flight bar) Trajectory! Vibration motor (held opposite the flight bar) 303.5 42.0 4-5 17.3 14.0 <3. After depositing a continuous photosensitive film on a substrate using the invention described in Section O1, the coating is then subjected to conventional operations used in the fabrication of printed circuit boards b. The film is exposed to chemical radiation, such as an arc lamp, through a mask having a circuit pattern.

In the case of positive resists, whether anionic or cationic, the exposed areas are dissolved and removed by acidic or alkaline developers, respectively.

In the case of negative resists, the unexposed material, whether anionic or cationic, is dissolved and removed by the developer. In either case, the remaining resist adheres to the substrate throughout the next etching step, where cupric or ferric chloride, or ammoniacal solutions dissolve the exposed copper. The resist is removed with an organic or aqueous stripper after the etching step.

This same technique is also applicable when using electrodeposited resists as plating resists. That is, the resist is applied onto a native conductive film. After writing, metal is plated in the lines formed after developing the resist, whereupon the resist becomes the sidewalls that define the image of the added metal.The resist is then stripped as described above.

[Brief explanation of drawings]

FIG. 1 shows an example of a method of carrying out the invention. l...-1--Motor 2-------M-Tank 3--Yoke 4--Rubber gasket 5---1 - Substrate 6 - - 1 - Coating bath 7 - - - 1 positive 8 - - - - Flight bar 9 - - - Clamp lo - - - - 1 - Flange 11 ------- Clip 12 ---- Air bubble

Claims (21)

[Claims] 1. A method of eliminating pinhole defects that occur during the electrodeposition process, which involves depositing an organic coating material on a conductive substrate and applying a continuous stream of energy sufficient to remove any air bubbles adhering to the substrate. The method, characterized in that it comprises the step of applying a vibratory force to the substrate. 2. The method of claim 1, wherein the organic coating material is anionic. 3. The method of claim 1, wherein the organic coating material is cationic. 4. The method of claim 1, wherein the conductive substrate is a copper clad laminate. 5. The method of claim 1, wherein the conductive substrate is a flexible metal foil. 6. The method of claim 1, wherein the conductive substrate is a rigid metal sheet. 7. 2. The method of claim 1, wherein said vibratory force is generated by a pneumatic motor. 8. 2. The method of claim 1, wherein said vibratory force is generated by an electric motor. 9. The sufficient energy vibration force is 60 per minute.
2. The method of claim 1, wherein the vibration range is 30,000 to 30,000 times. 10. 2. The method of claim 1, wherein the frequency and amplitude of the sufficient energy vibratory force is 3,000 vibrations per minute. 11. An improved method for making printed circuit boards, comprising the following steps: a. Providing a conductive substrate on which a photosensitive coating material is deposited by electrophoresis b. Imagewise exposure of the deposited coating material to a source of chemical radiation and treatment of said exposed photoresist with a suitable developer solution; c. The improved method includes performing an etch on the photoresist prior to removing the resist material, the improved method applying a continuous oscillatory force of sufficient energy to remove bubbles generated during the electrophoretic deposition process. The method further comprises depositing the photosensitive coating material as a continuous film without pinholes. 12. 1. An apparatus for electrodepositing an organic coating material onto a substrate, comprising: a. Bath of organic coating material b. A tank containing said bath c. a conductive substrate immersed in said bath; d. a potential source connected to the substrate e. an electrode in contact with the coating bath and connected to an opposite pole of the power source; and f. The apparatus, characterized in that it includes means for selectively applying sufficient vibratory force to the substrate to remove air bubbles adhering to the substrate. 13. The means for selectively applying the vibrational force further comprises: a. a flight bar coupled to said substrate b. A clamp for holding the flight bar c. A yoke to which the clamp is attached and which is also in contact with the vibration source d. 13. The apparatus of claim 12, including a cushioning material between the tank and the yoke so that the tank does not vibrate. 14. 14. The apparatus of claim 13, wherein the vibration source is an electric motor. 15. 14. The apparatus of claim 13, wherein the vibration source is a pneumatic motor. 16. Claim 12: The surface of the conductive substrate is made of metal.
The device described. 17. 13. The apparatus of claim 12, wherein the conductive substrate is a copper clad laminate. 18. 13. The apparatus of claim 12, wherein the organic coating material is anionic. 19. 13. The device of claim 12, wherein the organic coating material is cationic. 20. Claim 1, wherein the organic coating material is photosensitive.
2. The device according to 2. 21. A product produced by the method of claim 1.